Photocatalytic removal of monoterpenes in the gas phase. Activity and regeneration

Abstract

We show the photocatalytic removal of various monoterpenes such as β-pinene, α-pinene, camphene and limonene in the gas phase as a function of the reaction temperature, from room temperature to 80 °C, taking also into account the thermal catalytic isomerization occurring on TiO₂ surfaces. The on-stream behaviour showed an initial plateau with total monoterpene removal followed by a progressive deactivation, associated to the surface poisoning by partially oxidized intermediates. Effective regenerative treatment could be performed under UV-A illumination with an oxidative humid air flow, for oxidizing the detrimental organic reaction intermediates into CO₂. Deactivation phenomena were studied as well as the optimization of regeneration treatments, both depending on the surface density of the TiO₂ coating, and we proposed that non-illuminated TiO₂ layers could be involved for explaining the interesting activity/deactivation behaviour pattern observed. We tried to evidence that reaction–regeneration cycles could be put forward to hold a continuous high efficiency monoterpene removal.